The invention relates to an adjusting device for a cable pull of a parking brake, wherein when the parking brake is disengaged, a pulling element capable of being connected to the cable pull and designed as a threaded spindle, can be tightened relative to a housing on account of the prestressing of a spring onto a spindle nut engaging around the threaded spindle.
DE-A41 42 290 describes an adjusting device for a cable pull of a parking brake with a housing, wherein a pulling element is designed, in a first section, with a first external thread and, in a second section, with a second external thread, the two threads having different pitches. Provided on the first section of the pulling element is a first spindle nut, which is designed with an internal thread and, in its outer circumference, has a thread-like groove in which a carry-along element engages, the latter being guided axially in the housing and being prestressed by a first spring counter to the run-out direction of the cable pull. The first spring is supported against a flange section, of which the rear side is subjected to the action of a second spring, which is supported against a second spindle nut, which rides on the second threaded section with a corresponding thread pitch. The second spring acts counter to the first spring. Under the loading of the resultant of the first spring and of the second spring, the pin is displaced in the circumferential groove of the first spindle nut and the latter is rotated, as a result of which the pulling element and the cable pull adjoining the latter are tensioned by displacement of the pulling element. A blocking arrangement is provided for the transportation of the adjusting device. The first spring is designed as a compression spring, of which the stressing force decreases as the spring excursion increases, with the result that it is necessary for the abutment of the first spring to be adjusted via a complicated design with a plurality of thread pitches and a plurality of spindle nuts. For this purpose, it is necessary for a second spring partially to eliminate the restoring force of the first spring counter to the prestressing of the latter. The displacement of the housing is difficult since, as a result of the pulling element tilting, the spindle nuts are blocked and adjustment is no longer possible. Furthermore, the displacement distance of the pulling element is limited on account of the two different circumferential threads, with the result that only comparatively small displacement movements, and thus a small amount of follow-up tensioning of the cable pull, is possible. The adjusting device can only be secured with additional outlay upon actuation of a parking brake.
EP-A-0 914 996 describes a handbrake which is equipped with an automatic adjusting device, wherein the cable pull of a parking brake can be adjusted, via a gear/rack system, by means of two springs arranged one behind the other, of which one is a helical spring and the other is a wrap spring, the known arrangement taking up a large amount of space and, furthermore, requiring high-outlay guidance for the toothed segment. Furthermore, adjusting steps are always provided in the case of rack/gear systems, whereas it would be desirable to have continuous adjustment which correspondingly accommodates the elongation of the brake cable.
WO-A-98 57 832 describes a locking arrangement for the cable-pull adjustment of a brake cable of a parking brake, wherein a toothed-surface pulling element is prestressed on account of the prestressing of a spring counter to the loading of the brake cable and of the brake-actuating elements coupled thereto, it being possible for the toothed surface to be locked in the manner of a catch mechanism by a toothing formation, which is directed toward said surface, of a clamping element. The clamping element has a wedge-shaped head, which is supported against a wedge guide, likewise of wedge-shaped design, of a clamping housing and, on account of guide-pin ends which project laterally from the head and force the same to move along two ramps of the blocking housing, which are likewise of wedge-shaped design, is raised when the clamping element is displaced axially, with the result that the clamping element, at the same time, executes a movement in the direction away from the toothing formation. On account of a locking spring, the clamping element is prestressed into an engagement position for producing the catch mechanism, with the result that, when the parking brake is actuated, via this catch mechanism, the brake cable pull is tensioned. When the parking brake is disengaged, an angular extension of the clamping element, against which the locking spring is supported, strikes against a stop, as a result of which the clamping element, with the locking spring being subjected to stressing, is displaced axially and, on account of the guide, is also disengaged from the pulling element, as a result of which the effect of the catch mechanism is eliminated. When the parking brake is disengaged, the stop is actuated, with the result that release takes place whenever the parking brake is disengaged. Raising the brake-actuating lever of the parking brake results in tensioning of the brake cable, in its position, assumed on account of the position of the pulling element in accordance with the prestressing of the spring, in which it should not sag, for actuating the brake body, in that the locking spring displaces the clamping element, upon removal of the extension of the latter from the stop, in the direction of an effective catch mechanism of the toothing formations again. The known locking arrangement, on account of the coaxial design of the locking spring and of the spring for adjusting the brake cable, is susceptible to slippage of the pull rod. Furthermore, on account of the type of toothing formation, the locking only allows a limited number of adjustments of the catch mechanism, whereas it would be desirable to provide a larger number or to provide step-free latching positions. Furthermore, the toothing formation has to be designed as a sawblade toothing formation, with the result that a definite latching sound can be heard when the two parts are moved relative to one another.
It is an object of the present invention to provide an adjusting device, which easily allows continuous adjustment of a cable pull.
The present invention provides an adjusting device for a cable pull of a parking brake. The adjusting device includes a cable pull, a housing, a pulling element including a threaded spindle and capable of being connected to the cable pull, a spindle nut engaging around the threaded spindle, a supply reel having an axis of rotation parallel to an axis of the spindle nut, and a scroll spring acting on the spindle nut and on the supply reel. When the parking brake is disengaged, the cable pull is tightened relative to the housing using a prestressing of the scroll spring. When the parking brake is engaged the pulling element is retained relative to the housing.
The adjusting device according to the invention makes it possible for the cable pull to be adjusted continuously by virtue of the pulling element connected to the cable pull being tightened, it being possible for the spindle nut and the threaded spindle, for adjustment of a predetermined distance, on account of a corresponding pitch, to carry out the adjustment within any desirable route, which can preferably be adapted to a conventional aging-induced elongation of the cable pull. It has to be understood that the spindle is assigned, if appropriate, a torque support which, in addition to the attachment to the cable pull, ensures that the spindle is only displaced axially and is not rotated as well. The threaded spindle here passes through the housing without coming into contact with parts of the housing outside the spindle nut, with the result that the adjustment of the cable pull and/or of the threaded spindle is carried out axially exclusively on account of a rotary movement of the spindle nut, by the spring force acting thereon. The means for retaining the pulling element when the parking brake is engaged, or as the parking brake is being engaged, are necessary in order to prevent the cable pull from being relieved of loading by the threaded spindle rotating back as the parking brake is being engaged. It is possible for these means both to effect a force-fitting and/or form-fitting external engagement of the spindle nut and to be realized by a self-locking configuration of the spindle/spindle nut system. At the same time, it is possible to limit the displacement distance of the threaded spindle by an end stop or the like and thus to ensure that the cable pull is always tensioned following a certain tightening distance. The parking brake can be secured in a known manner, e.g. by a catch/toothed segment system.
The spring for acting on the spindle nut is designed as a scroll spring which, by virtue of its tangential introduction of force into the spindle nut, ensures a permanently applied torque and acts on a supply reel. This torque does not have to be large since, as a result of the thread, the force introduced is stepped down. Scroll springs have a flat spring characteristic and a negligible hysteresis, for which reason the torque which acts on the spindle nut is essentially constant over the entire length of the unwound scroll spring. It is advantageously possible here for scroll springs to be easily configured to the effect that they accommodate up to 100 turns, the number of turns over the elongation extent of the cable pull during the service life defining the number of spindle-nut turns which are to be correspondingly provided relative to the threaded-spindle section, and thus also allowing very flat pitches with correspondingly precise adjustment.
The supply reel, on which the scroll spring acts, is designed with a circular or more or less circular cross section, which has winding up on it those windings of the scroll spring which have been unwound from the spindle nut, which likewise preferably has a more or less circular outer circumference. The supply reel itself is accommodated in a rotatable manner, for example by way of shaft stubs mounted in corresponding bores, and can be moved, as far as possible, in a resistance-free manner, with the result that the force introduced is attributable exclusively, or predominantly, to the scroll spring. The diameter of the supply reel here may also be smaller than the diameter of the outer circumference of the spindle nut, and should be sufficiently spaced apart from the housing in order to be able to accommodate, if appropriate, a multiplicity of windings of the scroll spring.
The supply reel and the spindle nut expediently have axes of rotation which are parallel to one another and preferably to the longitudinal axis of the threaded spindle, particularly favorable tangential introduction of force by the scroll spring being ensured when the scroll spring winds up on the circumference of the spindle nut and on the supply reel in opposite directions, that is to say, as seen in cross section, the scroll spring is of S-shaped configuration in the transition region between the two outer contours. This makes it possible for relatively high forces to be transmitted to the spindle nut.
The spindle nut, the supply reel and the scroll spring are preferably arranged in a common housing part, which can be moved relative to the housing, which is arranged in a non-displaceable, if appropriate pivotable, manner on the brake-actuating lever or on a part projecting rigidly therefrom. The movement distance of the housing part is preferably limited here by lateral guides and/or an end stop, with the result that, ultimately, the housing part moves relative to the housing in the manner of an on/off switch, wherein with the housing part displaced, the adjusting device allows tensioning of the cable pull on account of the spindle nut being subjected to the spring action and, with the housing part brought into abutment with the housing, this being excluded.
The housing part is expediently prestressed into the release position relative to the housing by means of a compression spring, for example of a helical spring, with the result that rotation of the spindle nut and thus also of the threaded spindle is permitted whenever the parking brake has not been, or is not being, engaged. If, in contrast, the parking brake is engaged on account of an engaging movement of the brake-actuating lever, the spring is compressed such that the housing part and housing come into contact with one another and the capacity of the spindle nut to move freely is eliminated.
It is possible for the housing to be arranged rigidly on the brake-actuating lever, but it is preferable for the housing to be arranged pivotably on the brake-actuating lever, in order to ensure optimum cable run-out.
It is preferable for at least the housing or the spindle nut to have a friction or brake pad or Hirt serrations, these, when the housing part comes into abutment with the housing, preventing rotation of the spindle nut, as a result of which, when the parking brake is engaged, the brake cable is tensioned without the adjusting device yielding.
A particularly preferred configuration of the adjusting device according to the invention makes it possible to dispense with external means for locking the spindle nut for securing the threaded spindle when the parking brake is engaged, or to provide said means just as a safety measure, in that the forces correspondingly acting on the spindle/spindle nut system are coordinated with the pitch of the same such that, when the parking brake is disengaged, the cable pull can be adjusted on account of the action of the spring, whereas, when the parking brake is engaged, the thread flanks, which are in engagement with one another, are retained in a self-locking manner in relation to one another and spinning of the spindle nut is prevented on account of the self-locking. Force-fitting and/or form-fitting retaining means acting on the outside of the threaded spindle in the engaged state of the parking brake are then no longer necessary for fixing the threaded spindle or may be provided as additional securing means without actually being used on a regular basis. For example, when the parking brake is disengaged, the force acting on the cable pull for the follow-up tensioning of the spring is between 50 and 250 N, preferably approximately 100 N, whereas, when the parking brake is engaged, forces of far more than 1 000 N, expediently more than 2 500 N and preferably 5 000 N and above, are active, these giving rise to self-locking of the thread flanks of the threaded spindle and spindle nut.
Further advantages and features of the invention will become apparent from the following description and from the claims.